Television receiving apparatus



Decw 5, 19359. R. URTEL 2,182,326

TELEVISION RECEIVING APPARATUS Filed Dec. 20, 1935 INVENTOR RUPHF MTEL ATI'TORNEY Patented Dec. 5, 1939 TELEVISION RECEIVING APPARATUS Rudolf Urtel, Berlin, Germany, assignor to Telefunken Gesellschaft fiir Drahtlose Telegraphic m. b. IL, Berlin, Germany, a corporation of Germany 1 Application December 20, 1935, Serial No. 55,493 In Germany December 20, 1934 4 Claims. (Cl..1787.5)

- My invention relates to a method of and apparatus for correcting distortion in a transmitted television signal occasioned when scanning pic- 'ture elements representative of a rapid transition from light to dark or vice versa in the picture.

In all television transmission methods operating with constant velocity of scanning, the transmission of sharp details (rapid transition from bright and dark) is limited due to the limited size of the scanning openings of a Nipkow disc for the scanning or due to the limitation of the scanning luminous spot, in the case of cathode ray type transmitters.

In the present state of the art, the limitation set by the transmission means (with the band) is of secondary importance. Optical conditions (intensity of light) are opposed'to a reduction of the scanning spot below the size hitherto possible. Accordingly, there is a certain amount of impracticality attached to compensation of this type of distortion at the transmitter.

My invention provides a means whereby compensation for the aforementioned distortion is accomplished by developing at the cathode ray receiver a complementary signal which is representative of the frequency and amplitude of the video signal received, and utilizing this developed signal to both modulate and control the deflection of said cathode ray.

My invention will best be understood by reference to the accompanying figures in which:

Figure 1 represents the theoretical change in developed scanner or potential current which should occur if no distortion were present in the sharp transition between dark and bright in the image to be transmitted.

Figure 2 shows the actually developed current or voltage.

Figures 3, 4 and 5 are explanatory curves; and

Figure 6 is an embodiment of my invention.

Referring to Figure 1, there is shown the signal which theoretically should be developed at the scanner when the elemental section of the image undergoing scanning changes from black to white, or vice versa, depending on the reference to which the signal is developed. Assuming an increase in developed potential represents an increase in brightness of the object, the value of potential should rise vertically with respect to time on the current or voltage-time curve. This varies from the actual conditions as limited by the size of the scanning openings in a Nipkow disc or the size of concentrated beam in a cathode ray tube.

the signal produces an additional deviation of the ray composing the image, since the normal deviation as such is carried out with constant velocity. In receivers with cathode ray tubes this may, for instance, be accomplished by applying the additional potential to the line deviation plates.

Figure 4 shows the distance-time diagram of the ray without and with additional deviation an and 3:2, respectively.

Figure 5 indicates the intensity course throughout the path and again without (I1) and with (I2) additional deviation. These two curves show the increase in the sharpness of the contours obtained by the additional deviation. But it a should be borne in mind that the efiective brilliancy H observed b'y'the eye is proportional to the intensity I, and proportional in the inverse sense to the recording velocity v." The addi tional deviation however also changes the recording velocity in accordance with the second differential quotient of the intensity with respect to-time (Figure 4, v1, v2)

The course of the brilliancy as obtained from the course of the intensity by considering the velocity is included in Figure 5 (H1 without, and Hz with additional deviation). A comparison of the curves H1 and H2 shows the degree of the increase in sharpening the transition from dark to brilliant that can be obtained in this fashion (the transitions from brilliant to dark will be influenced to the same manner).

By means of the additional deviation control through a potential corresponding to g dt only one example of embodiment of the idea of the invention is shown. The invention can be carried out by means of all arrangements known for line control such, as for instance, in case of cathode ray receivers, the influence upon the resistance of the charging tube for the line deviation by a value derived from the course of the intensity. r

Referring to Fig. 6, there is shown a cathode ray tube with an embodiment of my invention. The picture signals are fed to an amplifier tube In, in this case a screen grid tube. Joined to the anode of the tube is a frequency responsive device, in this case an inductance II and an anode potential supply l4.

Also joined to the anode of the tube Land in parallel with elements H and I4, is a condenser l2 and a resistance l3. Potential supply 9 biases the element 4a positively with respect to the cathode of the cathode ray tube.

The cathode ray tube l contains a cathode 2, control grid 3 and anode 4. For the purpose of simplicity only the horizontal. deflecting coils 5 have been illustrated. In addition to the horizontal deflecting coils 5, there are supplementary horizontal deflecting means 6 which are electrostatically operated. An additional anode structure 4a is joined to the condenser IZ-resistance l3 circuit, as well as deflecting plates 6.

The incoming video signal is impressed on the control grid of tube Ill and there appears 'g a corresponding signal of increased amplitude in the output circuit. The condenser l2 will then be charged to a value dependent on the amplitude of the signal and the frequency response of the anode circuit. This signal will retard the deflection of the cathode ray beam and will modulate the recording velocity of the 'beam, auxiliary deflecting means, means for deriving from the received video signal an auxiliary signal bearing a proportionality to the first derivative of the amplitude of said video signal,

and means for affecting the deflection of the cathode raybeam by at least a portion of said derived signal.

2. In a television receiver, a cathode ray tube comprising an envelope including means for generating the cathode ray beam, means for accelerating said beam, electromagnetic means for deflecting the beam in one coordinate of its movement, auxiliary deflecting means for affecting the movement of the beam in the same coordinate as the electromagnetic means, an amplifier adapted to be energized by a portion of the received video signal, frequency responsive of optical reconstruction of said signals by means. of said developed quantity to correct thedistore,

tion in said transmitted signals.

4. Ina television receiver, a cathode ray tube comprising an envelope including means for generating, accelerating, and modulating a cathode ray beam, means for deflecting thebeam in at least one co-ordinate of movement, auxiliary deflectingmeans, a thermionic vacuum tube having anode, cathode and at least one control electrode, means for impressing received television signals onto the modulating electrode of said cathode ray tube and onto the control electrodecathode circuit of said thermionic tube, inductive means connected in the anode-cathode circuit of said thermionic tube, and impedance circuit connected substantially in parallel with said inductive member and subject to variations in potential across the terminals of said inductive member, and means for impressing the variations in potential across at least a portion of said impedance circuit onto said auxiliary deflecting means.

RUDOLF URTEL. 

